1. Field of the Invention
The invention relates in general to a memory and a method for fabricating the same, and more particularly to a NAND type dual bit nitride read only memory (also called N-bit) and a method for fabricating the same, that a process sequence is fully compatible with a complementary metal-oxide semiconductor (CMOS) process.
2. Description of the Related Art
N-bits (nitride read only memory) can be classified as NOR type N-bit and NAND type N-bit. NOR type N-bit features in capacities of storing instructions, prompt execution, rapid reading, large memory cell area and small storage capacity. NOR type N-bit is mainly applied in mobile phones, optical disk drives, hard disks and printers. NAND type N-bit features in data storage but not instruction storage. Also, the NAND type N-bit has small area addition, the barrier diffusion oxide 22 are formed above the buried bit lines 20 to isolate the word lines 24.
The memory cells 32 are formed by the word lines 24, the buried bit lines 20, and the ONO stack structures 17. The memory cells 32 form as a cell array as shown in FIG. 1A. Each of the memory cells 32 includes the first bit storage nodes 34 and the second bit storage nodes 36. The first bit storage nodes 34 and the second bit storage nodes 36 of every memory cell 32 are spaced at intervals along an extension direction of the word lines 24, so that the area of every memory cell 32 can be larger.
Referring to FIG. 2A to FIG. 2E, a cross-sectional view of procedures of a fabricating method for a NOR type dual bit N-bit of FIG. 1B is shown. Firstly, the silicon substrate 10 is provided and an ONO layer 16 is formed on the silicon substrate 10. The ONO layer 16 includes the bottom oxide layer 11, the silicon nitride (SiN) layer 13, and the top oxide layer 15 from the below to the top in order. Subsequently, a patterned photoresist layer 18 is formed on the ONO layer 16. And also the spaced and parallel buried bit lines 20 are formed by utilizing an ion implantation process. The buried bit lines 20 are formed in the silicon substrate 10, which is not covered by the patterned photoresist layer 18 as shown in FIG. 2B. Ion implantation is applied to form the buried bit lines 20, which includes the steps of: consequently influenced.